Method and Device for Ascertaining a Positional Deviation of a Rotational Body

ABSTRACT

The invention relates to a method and an apparatus for simultaneously ascertaining surface parallelism, axial perpendicularity and rotational surface runout of a rotational surface capable of rotating about a rotation axis relative to a reference surface. According to the invention, at least three distance sensors are provided which are stationary with respect to the reference surface and which have a measuring direction perpendicular to the reference surface and in the direction of the flat face of the rotational body. The distance sensors transmit distances ascertained during the rotation of the rotational body to an evaluation device, wherein an axial perpendicularity, a rotational surface runout of the rotational body and a surface parallelism can be ascertained from said distances. Prior to measuring the rotational surface runout, the angular deviation of the rotational surface is first ascertained.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage of International Application No. PCT/DE2018/100002, filed on Jan. 3, 2018. The international application claims the priority of DE 102017114378.5 filed on 2017 Jun. 28; all applications are incorporated by reference herein in their entirety.

BACKGROUND

The invention relates to a method and an apparatus for ascertaining a positional deviation of a rotational body capable of rotating about a rotation axis relative to a reference surface, in particular for simultaneously ascertaining at least axial perpendicularity and rotational surface runout.

A special challenge in the field of the invention consists in the fact that, although various geometrical and positional tolerances of the assembled components add up to a unitary error pattern, the causes are nevertheless to be ascertained and analyzed separately.

An important error to be ascertained is a deviation from the perpendicularity between the rotation axis of the rotational body and the reference surface, said error corresponding to at least an average deviation of the parallelism of the reference surface and a flat face of the rotational body. For better differentiation, this positional deviation will hereinafter be referred to as axial perpendicularity.

Furthermore, the current angle between the rotating surface and the immobile reference surface may vary during the rotation if there is a deviation in the perpendicularity between the rotating surface and the rotation axis and thus a rotational surface runout.

A runout related error may be caused not only by tolerances regarding the planarity of the measured flat face but also by the parallelism of the two flat faces of the rotational body relative to one another, which will hereinafter be referred to as surface parallelism for better differentiation. Deviations thereof result in a varying thickness along the circumference and at various radii of the rotating object.

All the aforesaid positional tolerances, i.e. axial perpendicularity, rotational surface runout and surface parallelism, are closely interrelated; for better understanding, refer to FIGS. 12a, 12b and 12c , which schematically illustrate axial perpendicularity, rotational surface runout and surface parallelism, respectively.

It is therefore difficult to ascertain one of these positional tolerances separately, in particular after various tolerances have added up in the assembled overall system. However, an exceedance of these tolerances is highly disadvantageous since the position of the rotational body relative to the reference surface is usually important, with the disadvantageous effects, while differing depending on the application, in most cases resulting in undesired vibrations.

An important field of application for ascertainment of axial perpendicularity and the other aforesaid values relates to disc brakes since the position of the brake disc relative to the caliper is important. Otherwise, a non-uniform transfer of the forces occurring during braking into the caliper, the caliper seat and ultimately the axle results causing undesired vibrations in the overall system.

Various solutions are known in the prior art which address the problem of measuring a rotating surface with respect to a surface that is immobile relative to the rotating system.

For example, German patent publication no. DE 198 53 078 C1 describes a measuring device and a method for simplified inspection of brake discs for disc runout and concentricity. For this, a shaft is rotatably supported on a bearing block, and a support for the brake disc is provided on the shaft. Mounted in this manner, the brake disc is rotated while disc runout and concentricity are checked on both flat faces and the outer cylinder surface using measuring devices. However, this inspection only yields results related to the brake disc itself. Proper concentricity or runout with respect to a further surface, such as a caliper seat, are not provided. Moreover, no further values are ascertained besides concentricity and runout.

Published German patent application no. DE 10 2011 002 924 A1 likewise relates to a method for identifying brake disc runout during braking. In this respect, this method is already closer to the practical use of the brake disc than the method cited above. This is because the braking pressure, or a variable dependent thereon, is measured during a braking operation using a sensor. The obtained sensor signal is then examined with respect to vibrations present therein. These vibrations then allow inferences regarding disc runout, which, however, does not necessarily originate from the brake disc itself. The error may also lie in the overall mounting system of the brake disc. A reference to a surface which is immobile relative to the rotating system, i.e. the brake disc, is thus established. However, the proposed method cannot ascertain any further information but is limited exclusively to an essentially qualitative statement with respect to disc runout. More importantly, however, the identified problems cannot be traced back distinctly to a mechanical malposition of the brake disc.

Published German patent application no. DE 10 2004 017 172 A1 describes a solution for measuring an object for measurement. According to this document, at least one reference structure is provided for the definition of a stationary object coordinate system, so that ultimately a complete contour of the object for measurement can be determined with the aid of an evaluation unit. However, the ascertainment of the complete contour of the object for measurement does not allow statements on concentricity or similar relevant data of the rotating surface with respect to an immobile surface.

In a similar manner, the solution according to published German utility model no. DE 20 2005 018 753 U1, which discloses a measuring device having profile sensors for geometrical quality inspection of wheelsets for railway vehicles, allows the mapping of the running profile of a railway wheel which is mounted in the measuring device as a complete wheelset. However, this document also fails to allow for statements with respect to an immobile surface, for example with respect to the subsequent mounting of the wheelset on the car.

Published German patent application no. DE 10 2014 006 151 A1 describes a method for measuring the concentricity of a machine tool and a machine tool configured for performing said method. A device operating with optical measuring radiation, in particular for interferometric distance measurement, detects deviations from the concentricity of the machine tool. Through automated adjustment of balancing weights within the chuck or the main spindle of the machine tool, the concentricity deviations so ascertained can be compensated via suitable actuators directly and during the processing of a workpiece.

Published European patent application no. EP 1 074 323 A1, which likewise relates to the field of machine tools, discloses an apparatus with an adjustable clamp system for holding a workpiece centrally with respect to its rotation axis. The concentricity of the clamp system is measured by a distance sensor. To enable precise centering, the clamp system is to be displaced relative to the rotary bearing device in an automatically controlled manner. However, the proposed apparatus enables only examination of the concentricity, without the possibility to ascertain further relevant data.

Numerous solutions are known for measuring the concentricity at machine tools, for example from DE 17 87 380 U, DE 197 53 426 A1 or DE 32 33 914 A1.

SUMMARY

The invention relates to a method and an apparatus for simultaneously ascertaining surface parallelism, axial perpendicularity and rotational surface runout of a rotational surface capable of rotating about a rotation axis relative to a reference surface. According to the invention, at least three distance sensors are provided which are stationary with respect to the reference surface and which have a measuring direction perpendicular to the reference surface and in the direction of the flat face of the rotational body. The distance sensors transmit distances ascertained during the rotation of the rotational body to an evaluation device, wherein an axial perpendicularity, a rotational surface runout of the rotational body and a surface parallelism can be ascertained from said distances. Prior to measuring the rotational surface runout, the angular deviation of the rotational surface is first ascertained.

DETAILED DESCRIPTION

The object of the present invention is thus to propose a method and an apparatus for ascertaining a positional deviation, at least axial perpendicularity and rotational surface runout, of a rotating surface with respect to a surface which is immobile relative to the rotating system.

This object is achieved by a method for simultaneously ascertaining axial perpendicularity and rotational surface runout of a rotational body capable of rotating about a rotation axis relative to a reference surface. According to an advantageous modified embodiment, the surface parallelism of the two flat faces of the rotational body is also ascertained, which will accordingly not exceed a tolerable degree of thickness variations. The rotation axis is preferably oriented perpendicular to the reference surface, especially when the reference surface is a caliper seat and the rotational body is a brake disc.

According to the invention, at least two distance sensors are provided which are stationary with respect to the reference surface, have a measuring direction perpendicular to and in the direction of a first flat face of the rotational body, and measure the distance from the flat face. The distance sensors transmit distances of various points from the first flat face of the rotational body ascertained during the rotation of the rotational body, including rotation data, i.e. the respective rotation angles, to an evaluation device, wherein an axial perpendicularity, a rotational surface runout of the flat faces of the rotational body and a surface parallelism can be ascertained from said distances. Further, prior to determining the rotational surface runout and the axial perpendicularity, the angular deviation of the flat faces is first ascertained. In a simplified embodiment, the rotation data, i.e. the respective rotation angles, are dispensed with, and a minimum and a maximum of the measured distances, and thus a largest and a smallest angular deviation, are instead included in the calculation by the evaluation device.

A rotational surface capable of rotating relative to a reference surface in the sense of the present invention is, for example, a marine screw propeller which is rotatable as a rotational surface relative to the bearing block inside the vessel. Other examples are the rotor of a wind power station as a rotational surface relative to the nacelle, the rotor of a helicopter, a gas or steam turbine, or a jet engine.

Due to the fact that the axial perpendicularity and the rotational surface runout of the flat faces of the rotational body relative to the reference surface remain within specified tolerances, and this can be checked in a quick and effective manner, the functional reliability of the respective applications is improved considerably. After all, in the case of a disc brake, too large deviations in the axial perpendicularity relative to the caliper result in undesired vibrations once the brake is actuated and the brake pads rest against the brake disc. With the method according to the invention, an ascertainment as to whether tolerances have been exceeded can already be made prior to the installation of the steering knuckle assembly or the axle assembly. In such a case, the defective assembly is not even installed but is immediately reworked until the specified tolerances are met. Expensive reworks on the completed vehicle or complaints are thus prevented.

Moreover, at least one further distance sensor is provided which is oriented towards a second flat face of the rotational body. If an evaluation device combines the measured values of this sensor with those of a sensor directed towards the first flat face, the surface parallelism of the rotational body can additionally be ascertained, and thickness variations can be determined.

According to an advantageous modified embodiment of the invention, at least one distance sensor is provided as a laser measuring sensor. Other distance measuring techniques, such as radar beams, may be considered as alternatives.

However, configurations in which at least one distance sensor is provided as a capacitive proximity sensor have proven to be particularly advantageous. This also allows, for example, measuring brake discs made of ceramics. Also, this results in extremely high precision, enabling measurements of deviations down to 10 nm. In addition, a capacitive proximity sensor only requires very little installation space, so that the size of the overall apparatus can be reduced considerably.

According to a preferred application of the present invention, a brake disc of a disc brake mounted to a steering knuckle assembly or an axle assembly is provided as the rotational surface, which brake disc is to be examined as to axial perpendicularity, rotational surface runout and surface parallelism of the brake disc relative to a caliper seat as the reference surface in the sense of the present invention. According to the invention, the plane of the caliper seat, which accordingly constitutes a reference surface, is projected to the tilting point at the rotation axis.

Particular benefits may arise from configurations in which at least three distance sensors are provided, two of them at a flat face of the brake disc, which sensors are rigidly attachable to the caliper seat and can provide a measurement result to an evaluation device during rotation of the brake disc. The measurement during rotation of the brake disc provides the possibility of ascertaining the maximum malposition, i.e. the angular deviation, whereas in the case of conventional measurements in a stationary state only the current angular deviation present in the respective position of the brake disc can be ascertained.

A further aspect of the invention relates to an apparatus for simultaneously ascertaining axial perpendicularity and rotational surface runout of a rotational surface capable of rotating about a rotation axis relative to a reference surface. According to the invention, at least two distance sensors are positioned which are stationary with respect to the reference surface and have a measuring direction perpendicular to and in the direction of a first flat face of the rotational body, wherein the distance sensors transmit ascertained distances from the measured flat face of the rotational body to an evaluation device. The evaluation device is configured such that it can ascertain an axial perpendicularity and a rotational surface runout of the rotational body and, if a third distance sensor is used on the opposite second flat face, also a surface parallelism. In a preferred embodiment, the rotation axis of the rotational body is oriented perpendicular to the reference surface. Accordingly, configurations are advantageous in which first distance sensors are arranged to act on a first flat face and/or second distance sensors are arranged to act on a second flat face of the brake disc.

According to a particularly advantageous embodiment, at least three distance sensors are arranged to act on the first flat face, e.g. an inner side, and two distance sensors are arranged to act on the second flat face, e.g. an outer side, of the brake disc. With five distance sensors, brake discs having various diameters can be inspected on one measuring device by activating or sampling the sensors that are positioned closest to the edge of the respective brake disc. The distance sensor closest to the edge preferably has a distance of 10 mm from the edge of the brake disc.

Further, configurations in which the measuring direction runs perpendicular to the reference surface have proven to be beneficial in disc brake related applications.

Advantageously, at least one distance sensor is configured as a laser measuring sensor or as a radar beam emitter. Configurations in which at least one distance sensor is configured as a capacitive proximity sensor are particularly advantageous. This also allows measuring brake discs made of ceramics. Also, this results in extremely high precision, enabling measurements down to 10 nm. In addition, a capacitive proximity sensor only requires very little installation space, so that the size of the overall apparatus can be reduced considerably.

Further advantages result from configurations in which a plurality of distance sensors is provided to act on the inner side and a plurality of distance sensors is provided to act on the outer side of the brake disc.

Also, configurations have proven to be advantageous in which separate embodiments are provided for a continuous axle, i.e. an axle assembly, and individual wheel suspensions, i.e. a steering knuckle assembly, respectively. In the case of a continuous axle, in particular a rear axle, the entire axle unit is inserted into the apparatus according to the invention, whereas in the case of individual wheel suspensions the steering knuckle assembly of each vehicle side is inserted into the apparatus and connected to the housing carrying the distance sensors separately. A separate apparatus, i.e. a separate housing, is preferably provided for each vehicle side.

A contribution in achieving the object according to the invention is further made by a calibrating device which includes a master adjuster comprising a planar surface dimensionally accurate to the required tolerance limits and parallel to the orientation of the rotational body, and which can be connected to the apparatus as described above. This enables adjustment of the distance sensors and/or the connected evaluation device. A measurement standard, configured as a dimensionally accurate brake disc or a modifiable device for simulating brake discs of different sizes, serves to examine the master adjuster and the entire apparatus.

Configurations have proven particularly beneficial in which the master adjuster is connected to the apparatus as described above in an actively movable manner such that it can be pivoted into the measuring area automatically and the apparatus can be calibrated. This is done, for example, in regular time intervals and/or depending on external factors such as shocks or temperature changes. Such an automatable calibrating function is particularly important where the apparatus is employed within a largely automated production environment in series production.

A further aspect of the invention thus relates to a calibrating method for calibrating the apparatus according to the invention as described above, and thus for ensuring constantly correct measurement results.

The invention is explained in more detail below by way of a description of exemplary embodiments and their illustration in the corresponding drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a schematic side view of an embodiment of an apparatus according to the invention for simultaneously ascertaining axial perpendicularity, rotational surface runout and surface parallelism, illustrating the position of a rotational surface capable of rotating about a rotation axis relative to a reference surface;

FIG. 2 shows a schematic front view of an embodiment of an apparatus according to the invention for simultaneously ascertaining axial perpendicularity, rotational surface runout and surface parallelism;

FIG. 3 shows a schematic perspective view of an embodiment of an apparatus according to the invention for simultaneously ascertaining axial perpendicularity, rotational surface runout and surface parallelism;

FIG. 4 shows a schematic illustration of the function of an apparatus according to the invention for simultaneously ascertaining axial perpendicularity, rotational surface runout and surface parallelism;

FIG. 5 shows a schematic front view of an embodiment of an apparatus according to the invention for simultaneously ascertaining axial perpendicularity, rotational surface runout and surface parallelism, including the evaluation device and the calibrating device;

FIGS. 6 and 7 show schematic perspective views of an embodiment of an apparatus according to the invention for simultaneously ascertaining axial perpendicularity, rotational surface runout and surface parallelism during use on an axle assembly;

FIGS. 8 and 9 show a schematic perspective view of an embodiment of an apparatus according to the invention for simultaneously ascertaining axial perpendicularity, rotational surface runout and surface parallelism at a steering knuckle assembly with closed and open cover, respectively; and

FIGS. 10 and 11 show an axle assembly 36 with an embodiment of an apparatus according to the invention; and

FIGS. 12a to 12c show a schematic illustration of the positional tolerances in the sense of the present invention: axial perpendicularity, disc runout and surface parallelism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic side view of an embodiment of an apparatus 1 according to the invention for simultaneously ascertaining axial perpendicularity, rotational surface runout and surface parallelism. Also shown is the position of a rotational body 30 capable of rotating about a rotation axis relative to a reference surface 11 connected to the housing 10. In the illustrated embodiment example, a caliper seat of an axle assembly 36 or a steering knuckle assembly 38 (see FIGS. 6 to 11) is provided as the reference surface 11. The reference surface 11 and the rotational body 30 are illustrated as invisible edges using dashed lines as they are covered by the housing 10. The housing 10 is connected to the reference surface 11 via connecting elements 12, preferably through a threaded connection or through bracing using bracing means.

Accordingly, the rotational body 30 is a brake disc, which is in this view illustrated as invisible edge using dashed lines as it is covered by the housing 10. The measuring points MP1, MP2 and MP3 are measured by the distance sensors 20, 22 and 24 at a first flat face, i.e. a surface of the rotational body 30. In addition to the distance sensor 22, a distance sensor 22′ is provided. Which one of the two distance sensors is used in a particular case depends on the diameter of the rotational body 30 since the measurement at the measuring point MP2 is to be performed near the outer circumference. The measured values are transmitted to an evaluation device 40 (see FIG. 5). The distance sensors 20, 22 and 24 are each fixedly connected to the housing 10 using a respective sensor holder 14.

FIG. 2 shows a schematic front view of an embodiment of an apparatus 1 according to the invention for simultaneously ascertaining axial perpendicularity, rotational surface runout and surface parallelism, in which the sensors 20 and 22 and 22′, respectively, are shown on the housing 10. The housing 10 is further provided with a handle 16 to facilitate the transport of the apparatus 1 to the point of installation. Once the apparatus 1 has been positioned at the point of installation, in particular a steering knuckle assembly or axle assembly and its caliper seat, they are connected to the apparatus 1 via connecting elements 12. As can be seen in the illustration, the connecting elements 12 have numerous boreholes and are thus suitable for use on various axle assemblies or steering knuckles, in particular the caliper seat respectively provided there.

FIG. 3 shows a schematic perspective view of an embodiment of an apparatus 1 according to the invention for simultaneously ascertaining axial perpendicularity, rotational surface runout and surface parallelism, with the illustrated embodiment corresponding to that of FIG. 2. The perspective illustration again shows the housing 10 with the handle 16 as well as the sensor holders 14 with the distance sensors 22, 22′ and 24. The connecting element 12 serves to connect to the reference surface 11, i.e. in the present case the caliper seat of the steering knuckle assembly or the axle assembly.

FIG. 4 shows a schematic illustration of the function of an apparatus 1 according to the invention for ascertaining a positional deviation of a rotation surface capable of rotating about a rotation axis relative to a reference surface, in this case of a brake disc 30 relative to a caliper seat. The illustration shows only a section of the brake disc 30, which does not include its rotation axis. The brake disc 30 is inclined relative to a zero line 32, which runs parallel to the caliper seat and represents a standard position, by an angular deviation 34. To ascertain the magnitude of the angular deviation 34 and to determine whether a provided tolerance range is exceeded, a distance A, A′ from a first flat face of the brake disc 30 is ascertained by the distance sensors 20 and 22 at two different measuring points MP1 and MP2. This is done using a sensor signal 26 and 26′, respectively, emanating from the distance sensors 20, 22 and 22′, respectively, which is directed towards the brake disc 30. Passing through the housing 10, which is provided with recesses 15 to this end, the sensor signal 26, 26′ reaches the brake disc 30 at the measuring points MP1 and MP2. The housing 10 is connected to the caliper 11 through the connection region 12. The distance sensors 20 and 22, or the measuring points MP1 and MP2, are arranged at different distances, i.e. the radius R, R′, from the rotation axis of the brake disc 30.

For a clear association of the ascertained angular deviation 34 with an actual angular deviation of the rotation axis from the perpendicular to the caliper seat 11 (zero line 32), it is not sufficient to ascertain the angular deviation only at two separate measuring points MP1, MP2. In view of this, the brake disc 30 is rotated about its rotation axis at least once and preferably multiple times during the measurement. During this process, the evaluation device 40 (see FIG. 5) receives not only the measured values from the distance sensors 20, 22 and 22′, respectively, but also the current rotation angle at the time of the distance measurement, which is transmitted, for example, from a drive of the brake disc 30 or a rotation angle sensor. The rotation angle sensor used may be, for example, a dummy wheel rim which is installed on the brake disc at the position of a wheel rim to be installed in the vehicle at a later point. To this end, it is provided with suitable circumferential marks that can be read out by the rotation angle sensor. In the simplest case, the five screws may be used as marks.

A measuring program executed in the evaluation device 40 retrieves the measured values of the respective distances from the brake disc via the sensors 20, 22 and 22′, respectively, and 24 if available and, based thereon and on the rotation data, i.e. the rotation angle of the brake disc, which is another measured value, calculates the angular deviations of the brake disc relative to the caliper seat 11 and the disc runout, i.e. the angular misalignment of the brake disc 30 relative to its rotation axis. In this manner, comprehensive information about the condition of the brake disc 30 in terms of axial perpendicularity, disc runout and surface parallelism relative to the caliper seat 11 of the steering knuckle assembly 38 or the axle assembly 36 can be obtained through ascertainment of the rotation angle dependent angular deviation 34.

To also obtain information about the surface parallelism of the brake disc 30, a distance sensor 24, which is not illustrated here, measuring a measuring point MP3 is provided on the opposite flat face of the brake disc 30. This sensor is, for example, arranged directly opposite the measuring point MP2, so that this also allows the evaluation device 40 to evaluate the measured values from the measuring points MP2 and MP3 in such a manner that deviations in surface parallelism, i.e. the thickness of the brake disc, can be determined along the entire circumference at least in the region of the measuring points. Advantageously, two distance sensors for the measuring point MP2 are then accordingly opposed by two corresponding distance sensors for the measuring point MP3. Additional distance sensors will provide an even more accurate picture of the surface parallelism.

FIG. 5 shows a schematic front view of an embodiment of an apparatus 1 according to the invention for simultaneously ascertaining axial perpendicularity, rotational surface runout and surface parallelism, including the evaluation device 40 and the calibrating device 44. Also shown is a rest position 42 in which the apparatus 1 can be placed safely when no measurement is to be performed.

The main function of the evaluation device 40 has already been described in connection with the preceding figures. In addition to this, however, the evaluation device 40 also performs the calibration of the apparatus 1, which is required in regular intervals in order to be able to always provide an accurate measurement result. For this, the brake disc is replaced with a rotational body 30 exhibiting either no or a known deviation from the zero line 32 (see FIG. 4), which is inserted and measured by the apparatus 1. The measured values obtained from the distance sensors 20, 22 and 22′, respectively, and 24 are used to calibrate the apparatus 1.

FIGS. 6 and 7 show schematic perspective views of an embodiment of an apparatus 1 according to the invention for simultaneously ascertaining surface parallelism, axial perpendicularity and rotational surface runout during use on an axle assembly 36. FIG. 6 illustrates the housing 10 in an open state, thus showing not only the sensors 20, 22 and 22′ but also the axle assembly 36. The latter comprises the caliper seat, which is not visible here and represents the reference surface 11 to which the housing 10 is screwed. The installed brake disc, which constitutes the rotational body 30, is now rotated about its axis in a defined manner, and the values meanwhile measured by the distance sensors 20, 22 and 22′ are transmitted to the evaluation device. Upon evaluation of the current angular deviation in the evaluation device, surface parallelism, axial perpendicularity and rotational surface runout of the brake disc relative to the caliper seat have been determined. FIG. 7 shows the same situation but with closed cover 18.

FIGS. 8 and 9 show a schematic perspective view of an embodiment of an apparatus 1 according to the invention for simultaneously ascertaining surface parallelism, axial perpendicularity and rotational surface runout at a steering knuckle assembly 38 with closed and open cover 18, respectively. The steering knuckle assembly 38 likewise comprises a caliper seat for attaching the housing 10 of the apparatus 1 after it has been positioned thereon using the handle 16. Upon attachment, the measurement of the brake disc, i.e. the rotational body 30, can commence. FIG. 9 additionally shows the sensors 20, 22 and 22′.

FIGS. 10 and 11 show an axle assembly 36 with the brake disc as rotational body 30 as well as the positioned and attached housing 10 of the apparatus 1. Also shown are the anchor plate 13, the caliper seat 11 and the connection region 12.

FIGS. 12a to 12c show a schematic illustration of the various positional tolerances that are ascertained according to the present invention. FIG. 12a shows the axial perpendicularity, with the rotation axis of the rotational body 30 running perpendicular to the (extended) reference surface 11. FIG. 12b shows the disc runout, i.e. the requirement is perpendicularity between the rotational body 30, or its flat faces, and its rotation axis, and deviations result in rotational surface runout. FIG. 12c shows the surface parallelism of the rotational body 30, i.e. parallel orientation of the two flat faces.

LIST OF REFERENCE NUMERALS

-   1 apparatus -   10 housing -   11 reference surface -   12 connecting element -   14 sensor holder -   15 recess -   16 handle -   18 cover -   20 distance sensor 1 -   22, 22′ distance sensor 2 -   24 distance sensor 3 -   26, 26′ sensor signal -   30 rotational body, brake disc -   32 zero line -   34 angular deviation -   36 axle assembly -   38 steering knuckle assembly -   40 evaluation device -   42 rest position -   44 calibrating device -   46 master adjuster -   48 connection seat -   A, A′ distance -   MP1 measuring point 1 -   MP2 measuring point 2 -   MP3 measuring point 3 -   R, R′ radius 

1. A method for ascertaining a positional deviation of a rotational body (30) capable of rotating about a rotation axis relative to a reference surface (11), said rotational body comprising at least one first flat face, characterized by simultaneously ascertaining at least axial perpendicularity and rotational surface runout of the first flat face of the rotational body (30), wherein at least two distance sensors (20, 22, 22′) that are stationary with respect to the reference surface perform measurements perpendicular to and in the direction of the first flat face of the rotational body (30), wherein the distance sensors (20, 22, 22′) transmit distances from the first flat face of the rotational body (30) ascertained at different points during rotation of the rotational body (30) to an evaluation device (40), wherein, based on the distances and taking into account the rotation angle of the rotational body (30), an axial perpendicularity and a rotational surface runout of the rotational body (30) can be ascertained in the evaluation device.
 2. The method according to claim 1, wherein at least one further distance sensor (24) is provided which is oriented towards a second flat face of the rotational body (30), so that a surface parallelism of the rotational body (30) can also be ascertained.
 3. The method according to claim 1, wherein at least one distance sensor (20, 22, 22′, 24) is provided as a laser measuring sensor.
 4. The method according to claim 1, wherein at least one distance sensor (20, 22, 22′, 24) is provided as a capacitive proximity sensor.
 5. The method according to claim 1, wherein a brake disc of a disc brake installed at a steering knuckle assembly (38) is provided as the rotational body (30) for ascertainment of surface parallelism, axial perpendicularity and rotational surface runout of the brake disc relative to a caliper seat as the reference surface (11).
 6. The method according to claim 5, wherein at least three distance sensors (20, 22, 22′, 24) are provided which are rigidly attachable to the caliper seat (11) and can provide a measurement result to an evaluation device (40) during rotation of the brake disc (30).
 7. An apparatus for simultaneously ascertaining axial perpendicularity and rotational surface runout of a rotational body (30) capable of rotating about a rotation axis relative to a reference surface, said rotational body comprising at least one first flat face, characterized in that at least two distance sensors (20, 22, 22′) are provided which are stationary with respect to the reference surface (11) and which have a measuring direction perpendicular to and in the direction of the first flat face of the rotational body (30), wherein an evaluation device (40) is provided to which distances from the first flat face of the rotational body (30) measured by the distance sensors (20, 22, 22′) as well as a rotation angle of the rotational body (30) with respect to the reference surface (11) are transmitted, wherein the evaluation device (40) is configured such that it ascertains an axial perpendicularity and a rotational surface runout of the rotational body (30) from the transmitted values.
 8. The apparatus according to claim 7, comprising at least one further distance sensor (24) which is oriented towards a second flat face of the rotational body (30) and measures the distance from the second flat face, so that a surface parallelism of the rotational body (30) can be ascertained from the measured values of the further distance sensor.
 9. The apparatus according to claim 7, wherein at least three distance sensors (20, 22, 22′) are provided to act on the first flat face and two distance sensors (24) are provided to act on the second flat face of the rotational body (30).
 10. The apparatus according to claim 7, wherein at least one distance sensor (20, 22, 22′, 24) is configured as a laser measuring sensor.
 11. The apparatus according to claim 7, wherein at least one distance sensor (20, 22, 22′, 24) is configured as a capacitive proximity sensor.
 12. The apparatus according to claim 7, wherein separate embodiments are provided for an axle assembly (36) with a continuous axle and for a steering axle assembly (38) for individual wheel suspension, respectively.
 13. A calibrating device which includes a master adjuster comprising a planar surface dimensionally accurate to the required tolerance limits and parallel to the orientation of the rotational body (30), and which can be connected to the apparatus (1) according to claim 7, wherein the distance sensors (20, 22, 22′, 24) and/or the connected evaluation device (40) can be aligned.
 14. The calibrating device according to claim 13, wherein the master adjuster is connected to an apparatus for simultaneously ascertaining axial perpendicularity and rotational surface runout of a rotational body (30) capable of rotating about a rotation axis relative to a reference surface, said rotational body comprising at least one first flat face, characterized in that at least two distance sensors (20, 22, 22′) are provided which are stationary with respect to the reference surface (11) and which have a measuring direction perpendicular to and in the direction of the first flat face of the rotational body (30), wherein an evaluation device (40) is provided to which distances from the first flat face of the rotational body (30) measured by the distance sensors (20, 22, 22′) as well as a rotation angle of the rotational body (30) with respect to the reference surface (11) are transmitted, wherein the evaluation device (40) is configured such that it ascertains an axial perpendicularity and a rotational surface runout of the rotational body (30) from the transmitted values, in an actively movable manner such that it can be pivoted into the measuring area of the distance sensors (20, 22, 22′, 24) automatically and the apparatus (1) can be calibrated thereafter. 